Currently, superalloys are widely used for applications in which high stresses must be endured at elevated temperatures, for instance in the components of gas turbine engines, such as blades and vanes. Improvements in manufacturing methods have led to casting of components in single-crystal form, resulting in improved high-temperature lives and strength over conventionally prepared metallic materials that included a plurality of grains separated by grain boundaries.
Due to the improved performance of single-crystal superalloy components, the ability to withstand severe operating conditions is expected. However, one or more significant departures from single-crystal perfection may seriously limit the ability of a single-crystal superalloy component to perform under severe operating conditions, and may shorten the service life of the component. Because, the likelihood of fracture and separation along crystallographic boundaries around imperfections is increased, castings for turbine blades and vanes require close inspection for spurious grains and other crystallographic imperfections. The current industry practice is to use an etching process to reveal the spurious grains and crystallographic imperfections on the surface of single-crystal castings. After etching, the casting is visually inspected to evaluate the etched surface relative to the appropriate acceptance criteria for the intended use of the casting.
While etching processes have historically provided good grain contrast for revealing the external grain structure of equiaxed and polycrystalline directionally solidified superalloy castings, these etching processes tend to be inspector dependant, are time-consuming, and may result in dimensional nonconformance due to excessive stock loss, especially given the relatively thin walls of internally cooled components. Stock loss can be very significant if the overall etching process has to be repeated due to insufficient ‘readability’ of grain. Further, the etching processes may suffer issues with the presence of scale, with a lack of reflectivity, or with various confounding or masking effects such as anodizing iridescence (aka bluing), which may result in failure to reveal, identify, or locate imperfections, or in difficulty in revealing, identifying or locating imperfections.
Accordingly, it is desirable to provide methods and systems for inspecting single-crystal superalloy castings without etching. Also, it is desirable to provide methods and systems for inspecting single-crystal superalloy castings that use X-ray diffraction (XRD) to locate surface and subsurface imperfections. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings and this background of the invention.